Electromagnetic wave generator



Ag. 19, 1958 J. H. BRYANT 2,848,649

ELECTROMAGNETIC WAVE: GENERATOR 5 Fild Jan. 24, .1.952

BY @f4/* ATTCRNEY United States Patent O ELECTRoMAGNE'riC WAVE GENERATOR John H. Bryant, Nutley, N. 5., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Application January 24, 1952, Serial No. 267,983

Claims. (Cl. 315-39) This invention relates to the generation of electromagnetic waves and more particularly to means for generating for generating and/or amplifying electromagnetic waves in a gas discharge plasma.

In gas discharge ionized regions, called gas discharge plasma, there is a relatively high concentration of positive and negative ions in approximately equal quantity. A notable example of such a region is the positive column of a gas discharge. Normally such a region is highly conductive and, therefore, exhibits a relatively low average voltage gradient. In a low pressure gas discharge plasma (e. g. pressure less than 10-1 mm. Hg), the mean free path of the fast electron stream traversing the plasma is longer than the electrode distances. Areas will exist where the electron stream may set up oscillations within the positive column. At frequencies in the neighborhood of 1000 to 4000 megacycles per second for example, the fast stream of electrons present in any low pressure gas discharge traversing the plasma can interact favorably with intrinsic oscillatory fields in the plasma to result in a net transfer of direct-current kinetic energy to electromagnetic energy.

One of the objects of this invention, therefore, is to provide a device for utilizing this interacting relationship between an electron stream, or streams, and a gas discharge plasma to generate electromagnetic wave energy.

Another object of this invention is to provide means for the amplification of an electromagnetic wave propagated through a gas discharge plasma.

Briefly, in accordance with one embodiment of this invention, a direct-current electron stream is projected through a gas discharge plasma to assist in maintaining ionization of the plasma and also to establish oscillations therein. In another embodiment of the invention, electromagnetic waves are propagated through a gas plasma for retardation to substantially the velocity of the electron stream. The electromagnetic Waves extract energy from the direct-current electron stream and are thus amplified.

Another feature of this invention is the provision for a feedback oscillator circuit by taking a portion of the output power and feeding it back to the input coupling at proper phase. The feedback arrangement can be either internal or external to the gas discharge plasma.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a longitudinal section view of an embodiment of this invention to produce electromagnetic waves in a gas discharge plasma;

Fig. 2 is a longitudinal section view of an embodiment of this invention as a self-excited oscillator utilizing a waveguide output coupling;

KFig. 3 is a longitudinal section view of an embodiment of this invention as an electromagnetic wave amplifier with coaxial input and output couplings;

IFig. 4 is a longitudinal section View of an embodiment 2,848,649 Patented Aug. 19, 1958 of this invention as an electromagnetic wave amplifier utilizing waveguide input and output couplings; and

Fig. 5 is a longitudinal section view partly in block form of this invention as an amplifier having an external feedback arrangement.

Referring to Fig. l of the drawing, an' electromagnetic wave oscillator, according to the principles of this invention, is shown, comprising a discharge tube 1 enclosing an ionizable medium 2, such as mercury vapor, an electron beam forming unit 3, an anode 4, a repeller electrode 5, iand an output coupling 6.

The beam forming unit 3 comprises a heater 7 and thermionic cathode 8 which is at a ground potential. Grid 9 is biased positive with respect to cathode 8 4and in y conjunction therewith serves to ionize the mercury vapor in region 10 which furnishes a stream of electrons used as a source of direct-current kinetic energy which is converted to electromagnetic energy in region 11. A positive potential, larger than the potential applied to grid 9, is applied to the anode 4, which for purposes of illustration is shown 'as a cylindrical conductor. The positive column or gas discharge plasma will then be contained in region 11 within which the direct-current kinetic energy of the electron stream from region `10 is converted to electromagnetic energy.

Provided the grid has a line mesh width having holes the order of 0.15 cm. in diameter, 25 holes per cm, the voltage applied to the grid 9 closes the grid holes with ion sheets and stops the flow of electrons from cathode 8 to anode 4. When the grid voltage is correctly controlled, the gas discharge can be stabilized between the tired and unred condition. In this way it is possible to considerably increase and localize the arc voltage drop. Each electron from region 10 which reaches the positive column of region 11 is accelerated into region 11 with velocities corresponding substantially to the voltage gradient. Provided the pressure is low, these accelerated electrons have a mean free path longer than the electrode distances and form an electron beam. When this beam is reected by repeller electrode 5, oscillations result. Rellections take place when the repeller electrode is biased positively with respect to the cathode 8 but still negative with respect to the positive column in region 11. A coaxial loop coupling 6 is inserted in region 11 to pick up the radio-frequency energy and propagate it through coaxial cable 12. Thus the direct-current kinetic energy utilized to form an electron beam is converted to electromagnetic energy.

Referring to Fig. 2 of the drawing, a self-excited oscillator with waveguide output connections is shown. The oscillator of Fig. 2 has means similar to the oscillator of Fig. 1 for causing oscillations to take place in region 11, which comprises a beam forming unit 3, grid 9, code 4, and repeller electrode 5, all contained within an envelope 1. The repeller electrode 5 of Fig. 2 comprises a fine mesh grid 13 covering an opening in the waveguide 14. Part of the oscillating electrons in region 1-1 are passed by this repeller grid electrode 13 into the waveguide structure where they are then propagated to the load.

Referring to Fig. 3 of the drawing, an electromagnetic wave amplilier according to the principles of this invention is shown. The amplier comprises an envelope 1 having an ionizable medium therein, and a beam forming unit 15, grid 16, anode 17, repeller electrode 18, input coupling 19, and output coupling 20. The beam forming unit 15 in conjunction with grid 16 and anode 17 and repeller electrode 18 causes oscillations to take place in region 21 as heretofore explained. lf radiofrequency energy is propagated through the positive cOlumn 21 by means of input coupling 19 and is of a velocity substantially equal to the velocity of the oscillations in region 21, the radio-frequency input energy will pick up energyin the positive column and thus be ampliied(V The" wave amplifier utilizing wageguide'input andoutput cou-V plings according to the principles of thisinventionf is shown. The electrons accelerated into the positive column V21.by the beam forming unit'are caused to oscillate in a mannersimilar to that-heretofore described.

The .power connections forV the beam formingV unit-areV brought in 'through waveguide 25. .to thef heater:Y 26:

Quarter wave choke elements 27 are used to prevent elec:-

trical discontinuity inthe waveguide structure. The outputwaveguideZS'has an opening which is covered'by.

repeller-electrode 18 which allowsrsom'epart' of'theoscil-l lating electrons. to be propagated down waveguide struc.l

If the frequency of the radio-frequency'inputis substantially equal to the frequency ofthe. electron x ture 28.

oscillations taking place in region 21, thel ontputtfrom waveguide28v will be the equivalentof the ampliied'l radio-frequency input.

Referring toFig. 5 of the drawing, an electromagnetic wave amplifier having. an externalfeedback arrangement f according to the principles of this invention is shown. The amplifier comprises input coupling 23, beam forming unit 30, grid 31, anode 32, repeller electrode 33, output coupling 34,` feedback coupling 35, line stretcher 36,and

feedback input coupling 37. Beam forming unit 3G-1in conjunction with grid 31, anode 32, and repeller'electrode 33 causes the electron stream to oscillate inregion 38,. Quarter wave chokes 39 are utilized to permit direct-y current energy to be coupled to the beamY forming unitY without causing an electrical discontinuity Yin .waveguide structure 29. The oscillating output from regionz'38 is passed by repeller electrode 33 into output waveguide' coupling 34. Part of the output is picked up by coaxial coupling loop 35 and propagated to coaxial couplingrloop 37 where it is combined with the radio-frequency-inpilt from waveguide 29.*and propagated through region-38.1

Line stretcher 36 is providedin the coupling between'outputand inputwaveguides to insure that the energyffedr back jfrom the output to the linput will arrive in proper:

phase.

While l havedescribed above thetprinciplesof myainrk vention in connection with certain embodiments, itis Yto be clearly understood that this description is made by 3 way of example only and lnot as a limitation to the scope of my invention as set forth in the objects'thereof'andv in the accompanying claims.

I claim:

l. A device for converting direct-current kinetic energyI to an electromagnetic wave energy comprising rmeans containing a volume of ionizable'material, means'ftoA establish a gas discharge plasma in said volume :of'ion-4 izable material including a source of electrons adjacent one end of said volume of ionizable material and meansv to form an electron beam from the electrons of said source of electrons and to accelerate said electron beam into said Volume of ionizable material, means spaced from said e source of electrons and adjacent the other end of said volume of ionizable material to repel said accelerated electron beam in a direction towardsaid source of electrons to establish electron oscillations in said gas discharge plasma to generate electromagnetic wave energy at aV frequency substantially equal to the frequency of said oscil- 1ati0ns,.and output coupling means adjacent said gas discharge plasma for coupling said electromagnetic wave energy therefrom.

2. A device according to claim l, wherein said output coupling means includes a coaxial connector having its innerconductor extending into the region of said gas discharge 1 plasma oscillations;

3. A device according" to claim l, wherein saidV output i coupling means includes a rectangular waveguide having an opening in one side adjacent said gas discharge plasma whereby said oscillatory energy will be propagated through said opening into said waveguide.

4. A device for converting direct-current kinetic energyV to electromagnetic energy comprising an electron discharge device having an envelope, a cathode serving as a source of electrons, an anode, an electrode spaced axially from said cathode, an ionizable medium within said envelope, means to vform an electron' beam from said source `of electrons and to' accelerate said electrons into said medium to produce a gas discharge plasma between said cathode.. and saidelectrode, terminal -means to bias said electrode to repelsaid accelerated electronbeam in a direction toward said cathode to thereby establish electron oscillations in said gas discharge plasma, and means adjacent said ionizable medium for coupling -oscillatory energyk from said plasma.

5. A device for converting directcurrent kinetic energy -l to electromagnetic energyV comprising-'an .electron 'dis-i charge device having an envelope, an electron '.emissive'.` cathode, an anode, an electrode spaced axially-from-said cathode, anionizable medium within said envelope, a l

grid betweenV said cathode. and said anode, a sourcefofelectronsy being disposed between said cathode'and 'said-k grid, terminal means to bias said anode to produce a gas. discharge-plasma between said grid and said electrode, to "f form the electrons of said ,source of electronsvk into an electronV beamA yand to accelerate said yelectron beam-1'l throughv said grid`into said gas discharge plasma, .terminal means to bias said electrode to repel said 'accelerateds electron beam in a direction toward said source of 'elec-v trons to thereby establish electron oscillations in said gas? discharge plasma, andv means adjacent .said ionizable-me` v dium for coupling'oscillatory energy. from said plasma.

6. A device for-converting direct-current kinetic energyl to electromagnetic energyf comprising .an ionizablejmeff dium, a plurality of electrodes including an anode,y a cathode, a grid, and a repeller electrode, means to couplel direct-current potential across said cathode and anode to ionize said medium thereby producing a gas-.discharge plasma adjacent to said anode, terminal means toapply a biasing Voltage to said grid with respect-tor said cathode and said anode to Vform the electrons of said source-ofi.

electrons into an electron beam and to accelerate said `ll` electron beam into said plasma toward said repel1er elec trode, terminal means to apply direct-current potentialv to said repeller electrode to repel saidaccelerated electrony j beam in a direction toward said cathode to thereby estab` lish electron oscillations in said plasma, and means ad; jacent said ionizable medium to couple oscillatory energy from said plasma. 7. An electromagnetic wave amplifier comprising means containing a volume of ionizable material, means f containing a volume of electrons adjacent said 'ionizable material, means to form the electrons of saidvolume .of electrons into an electron beam and to accelerate said I electrons into said material to establish a gas discharge plasma, means to repel said accelerated electron beam. in v a direction toward said volume of electrons to produce` electron oscillation in said gas plasma, means for conV electron beam from said cathode through said grid into said gas discharge plasma, terminal means to bias said electrode to repel said accelerated electron beam in a direction toward said cathode and thereby establish electron oscillations in said gas discharge plasma, output coupling means for said oscillations, a source of radio-frequency energy, and means to propagate saidV radio-frequency energy through said plasma at a phase velocity substantially equal to the Velocity of the electron oscillations.

9. An electromagnetic wave amplifier comprising a source of direct-current electrons, an ionizable medium, means to produce a gas discharge plasma in said medium including means to form an electron beam from said source of electrons and to accelerate said electron beam into said plasma, means to repel said accelerated electron beam in a direction toward said source of electrons to produce electron oscillations in said gas discharge plasma, means for coupling said amplier to a radio-frequency source, means to propagate said radio-frequency energy through said plasma at a phase velocity substantially equal to the velocity of said electron oscillation whereby Cil 6 the radio-frequency energy is ampliiied by absorption of energy from said electron oscillations, and means to feed back part of the output radio-frequency energy for propagation through said plasma.

10. A radio-frequency amplier according to claim 9, wherein said means to feed back part of said output radiofrequency energy includes means to control the phase shift in the radio-frequency energy fed back.

References Cited in the le of this patent UNITED STATES PATENTS 2,051,623 Tonks Aug. 18, 1936 2,081,429 Gaede May 25, 1937 2,308,523 Llewellyn Jan. 19, 1943 2,410,822 Kenyon Nov. 12, 1946 2,459,805 Fremlin ian. 25, 1949 2,538,267 Pierce et al. Ian. 16, 1951 2,557,961 Goldstein et al. June 26, 1951 2,636,948 Pierce Apr. 28, 1953 2,643,297 Goldstein et al une 23, 1953 2,653,270 Kompfner Sept. 22, 1953 

